1. Field of the Invention
The present invention relates to an external corner (arris) pole used as an exterior material of an external corner of a wall of a building, and an apparatus for chamfering the apex corner thereof.
2. Description of the Prior Art
Generally, as an exterior material of an external corner of a wall of a building, a projected corner column A as shown in FIG. 15 has been known (see JP 11-188294 A). For the production of the projected corner column A, usually a ceramic building board 1 having surface patterned parts (not shown) is used and the building board 1 is cut to have an appropriate width to give board pieces 1a, 1a, a lateral side of each board piece is cut at an angle (in many cases, at 45 degrees although not restricted thereto) (FIG. 16b), and cut surfaces 2, 2 are bonded with each other so that the surface pattern phases of the board pieces accord with each other at an apex corner 3 to give a body having an approximately L shaped cross-section (FIG. 16c).
During the bonding, misalignment may occur at the apex corner 3 or an adhesive may protrude off from the apex corner. In order to remove such problems, the apex corner 3 is subjected to chamfering 4 by a mechanical means such as a tenoner cutting machine (FIG. 16d). If the amount of an adhesive applied is too small, protrusion of an adhesive can be prevented. However, in this case, voids without an adhesive are liable to produce at the bonded part, which necessitates filling the voids by putty treatment or chamfering up to the part where the adhesive is embedded.
In either case, according to a conventional chamfering, a cut-processed surface 4 becomes a flat surface having a width as broad as about 10 mm to 20 mm as shown in FIGS. 15 and 16d and the chamfered part (cut-processed surface 4) has a color different from that of the surface of the board piece 1a, whereby coating is separately effected by using an apparatus such as that described in Patent Document 1.
As mentioned above, in a conventional projected corner column, an apex corner thereof has been subjected to chamfering over broad width using an apparatus such as tenoner cutting machine. Since a chamfered part is a wide flat surface having a width of approximately 10 mm to 20 mm, the part is highly visible even if it is coated. And since the chamfered part has a flat surface, the shade that generates on the part inevitably becomes different from that on a surface concavo-convex patterned part 5.
A projected corner column A is sometimes formed by bonding board pieces 1a, 1a each having, as a surface patterned part, an embossed pattern consisting of a plurality of convex stripes 6 and a plurality of concave grooves 7 both extending in a direction that intersects with a bonded surface as shown in FIGS. 17 and 18. In this case, a distance a between the tops of adjacent convex stripes 6, 6 is not more than about 30 mm on average, and is about 5 to 20 mm in many cases. Even in this form of projected corner column A, protrusion of adhesives Pa, Pb occurs in the vicinity of the top of convex stripe 6 and in the vicinity of the bottom of concave groove 7 as shown by a cross-section in the direction of the axis line of the bonded part in FIG. 18. In order to remove the adhesive Pa irregularly protruding in the vicinity of the top of the convex stripe 6, the apex corner 3 is subjected to chamfering with a mechanical means such as a tenoner cutting machine also in this case. Usually a chamfered part 8 having a rhombic flat surface is formed on the top of each convex stripe 6 as shown in FIG. 17 although the shape somewhat varies depending on the shape of the cross-section of the convex stripe 6.
When such projected corner column is installed as a corner material of an exterior material and exposed to a daytime sunlight, one side of the convex stripe 6 formed on each of the right and left board pieces 1a, 1a generates a light part S and the other side generates a shade part D to exhibit stereoscopic effect. Since a chamfered part 8 that is a rhombic flat surface as described above exists at the apex corner 3, the part gives a large light region Sa. The region Sa is not only highly visible and gives an odd sensation, but also breaks the continuity of the shade parts D of the convex stripes 6 on the right and left board pieces, thereby continuity of the pattern is lost. Due to such discontinuity, natural appearance is also lost.
Furthermore, an adhesive Pb protruded to the bottom of the concave groove 7 cannot be removed by chamfering with a mechanical means such as a tenoner cutting machine, and thus must be removed manually. However, in the case of a projected corner column that was produced by bonding board pieces 1a, 1a each having an embossed pattern consisting of a plurality of convex stripes 6 and a plurality of concave grooves 7 both extending in a direction that intersects with a bonded surface as shown in FIG. 17, the number of concave grooves 7 is necessarily large, and thus labors for removing the adhesive Pb are largely increased.